The wheel 1 of an automobile, and the rotor 2, which is a rotating member for braking of a disc brake as a braking apparatus, are supported so that they rotate freely by the knuckle 3 of a suspension apparatus using construction as shown in FIG. 8. That is, the outer ring 6 of a hub unit 5 for wheel support is fastened to the circular support holes 4 that are formed in this knuckle 3 by a plurality of bolts 7. On the other hand, the wheel 1 and rotor 2 are connected and fastened to the hub 8 of this hub unit 5 for wheel support by plurality of studs 9 and nuts 10. In addition, a double row of outer raceways 11a, 11b are formed around the inner peripheral surface of the outer ring 6, and a connection flange 12 is formed around the outer peripheral surface of this outer ring 6. This kind of outer ring 6 is fastened to the knuckle 3 by connecting the connection flange 12 to the knuckle 3 with the bolts 7.
The hub 8 comprises a hub body 13 and an inner ring 14. An outward facing mounting flange 15 is formed on part of the outer peripheral surface of the hub body 13, which is the bearing ring member of a rolling bearing unit for wheel support that is the target of the manufacturing process of the present invention, in the section that protrudes from the opening on the outside end of the outer ring 6. The ‘outside’ in the axial direction is the outside in the width direction of the vehicle when installed in the automobile, and is the left side in FIG. 18 and FIG. 19. Conversely, the ‘inside’ in the axial direction is the middle in width direction of the vehicle with installed in the automobile, and is the right side in FIG. 18 and FIG. 19. A positioning cylinder 16 called a pilot section is located on the outside end of the hub body 13 so that it is concentric with the hub body 13. The wheel 1 and rotor 2 are positioned in the radial direction by fitting them around this positioning cylinder 16, and connected and fastened to the outside surface of the mounting flange 15 by the studs 9 and nuts 10.
An inner raceway 17a is formed around the large-diameter middle section 26 of the cylindrical surface section that is formed around the middle part of the outer peripheral surface of the hub body 13 so that it faces the outside outer raceway 11a of the double row of outer raceways 11a, 11b; and similarly a small-diameter step section 18 is formed around the small-diameter section of the cylindrical surface section. This small-diameter step section 18, the middle section 26 and the step surface 31 that exists between these two sections 18, 26 form a stepped section. Also, the inner ring 14 fits around the small-diameter step section 18 of these sections. An inner raceway 17b is formed around the outer peripheral surface of this inner ring 14 so that it faces the inside outer raceway 11b of the double row of outer raceways 11a, 11b. This kind of inner ring 14 is fastened to the hub body 13 by a crimped section 19 that is formed by plastically deforming the inside end section of the hub body 13 outward in the radial direction. A plurality of rolling bodies 20 is located between each pair of outer raceways 11a, 11b and inner raceways 17a, 17b so that they roll freely. In the example shown in the figures, balls are used as the rolling bodies 20, however, in the case of a hub unit for a heavy automobile, conical rollers may be used. The openings on both ends of the cylindrical space where the rolling bodies are located are sealed by seal rings 21a, 21b. 
Furthermore, the example shown in the figures is a hub unit 5 for wheel support for drive wheels (the front wheels in the case of FF wheels, rear wheels in the case of FR and RR wheels, and all of the wheels in the case of 4WD wheels), so a spline hole 22 is formed in the center section of the hub 8. A spline shaft 24 that is formed on the outside end surface of the outer ring 23 of a constant-velocity joint is inserted into this spline hole 22. Together with this, a nut 25 is screwed onto the tip end of the spline shaft 24, and by tightening the nut 25, the hub body 13 is held between the nut 2 and the outer ring 23 of the constant-velocity joint.
Next, FIG. 19 shows a second example of a conventional hub unit 5a for wheel support, and is a hub unit for undriven wheels (rear wheels in the case of FF wheels, and front wheels in the case of FR and RR wheels). This second example of a hub unit 5a for wheel support is for undriven wheels, so a spline hole is not formed in the center section of the hub body 13a of the hub 8a. In the example shown in this figure, the inside end surface of the inner ring 14 is held by a crimped section 19 that is formed on the inside end section of the hub body 13a. This inside end surface of the inner ring can also be held by a nut that is screwed onto the inside end section of the hub body 13a. In that case, a male screw section is formed on the inside end section of the hub body 13a for screwing the nut onto. The construction and function of the other parts are the same as in the case of the hub unit 5 for wheel support described in the first example.
Incidentally, in the case of each of the hub units 5, 5a for wheel support described above, the construction of each is such that around the outer peripheral surface of the hub body 13, 13a, from the outside end side there is a positioning cylinder section 16, a middle section 26 for the outside outer raceway 17a, and a small-diameter step section 18 onto which the inner ring 14 is fitted. Besides plastic working such as hot forging or cold forging, cutting can be considered as the method for processing each of these sections. However, in order to improve processibility, maintain material yield and reduce costs, it is preferable that plastic working be performed. Moreover, of the types of plastic working, hot forging is capable of processing the object being processed in a soft state, so even though the formation load can be kept small, when taking into consideration the differences in thermal expansion, it is necessary to increase the fitting tolerance of the receiving and pressing molds, and it is difficult to maintain the precision of the shape and dimensions of the processed goods. Furthermore, in the case of hot forging, a decarburized layer occurs on the surface, so when there is a portion whose surface must be hardened by thermal processing, it is necessary to perform cutting in order to remove the decarburized layer. The machining allowance for the cutting process is somewhat large, so not only is the processibility reduced due to this cutting, but also the material yield becomes poor, which causes an increase in the processing cost of the hub body 13, 13a. 
Therefore, even though hot forging can be used for processing the aforementioned positioning cylinder 16 or mounting flange 15, when cost is taken into consideration, it cannot be used for processing the small-diameter step section 18. The reason for this is that the inner ring 14 must be securely fitted around this small-diameter step section 18 by an appropriate interference fit and the dimensions must be very precise, and to prevent the occurrence of fletching wear on the surface that fits with the inner ring 14, and form a quenched hardened layer on the surface. When these reasons are taken into consideration, the small-diameter step section 18 is formed by cold plastic working or cutting (turning). Of these, cutting produces a highly precise small-diameter step section 18, however increases the cost.
On the other hand, it is feasible to process the small-diameter step section 18 by ironing, which is a type of cold forging. In this case, as shown in (A) of FIG. 20, the material 27 to be processed into the hub body is pressed into a die 29 by a punch 28, and as shown in (B) of the same figure, the small-diameter step section 18 is formed on the tip end in the direction of pressing of the material 27. However, in order to process this small-diameter step section 18 by this kind of ironing process, the difference between the outer diameter DB of the material before being pressed into the die 29 and the outer diameter DA after being pressed (DB−DA) must be small, and the approach angle θ to the die 29 must be small. When either condition is not satisfied, the material 27 cannot be pressed into the die 29. More specifically, as shown in (C) of FIG. 20, the material 27 is not pressed into the die 29 and is compressed in the axial direction. Therefore, using conventional methods, it is difficult to process the small-diameter step section 18 with cold forging.
Japanese Patent Application Publication Nos. 2003-25803, 2003-291604 and 2004-74815 disclose inventions related to the structure of a hub comprising a positioning cylinder, mounting flange, middle section and small-diameter step section. However, all of the inventions disclosed in these patent applications are related to the structure of a hub for which it is easy to process or install the positioning cylinder or mounting flange, however do not suggest techniques that make it possible to process the small-diameter step section on the inside end of the hub by cold forging.